Piezoelectric vibrator and acceleration sensor using the same

ABSTRACT

Four piezoelecric elements are formed on both surfaces of a plate-shaped vibrating body. Two piezoelectric elements are formed to be opposite to each other at one side of the longitudinal center portion of the vibrating body. Another two piezoelectric elements are formed to be opposite to each other at the other side of the longitudinal center portion of the vibrating body. By applying a signal to the piezoelectric elements, the vibrating body is vibrated in a longitudinal direction. In this time, the vibrating body is vibrated in such a manner that longitudinal expansion and contraction take place simultaneously in a part of the vibrating body. By using such vibration, both longitudinal ends are not displaced in spite of the vibration of the vibrating body. The vibrating body can be used as an acceleration sensor by measuring the output voltages from the piezoelectric elements of the vibrating body.

This is a divisional, of application Ser. No. 08,202,017 filed Feb. 25,1994, pending.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a piezoelectric vibrator and anacceleration sensor, particularly, relates to a piezoelectric vibratorused for oscillator, filter and sensor, and relates to an accelerationsensor using the piezoelectric vibrator.

2. Description of the Prior Art

As a piezoelectric vibrator using the piezoelectric effect, there is thepiezoelectric vibrator which a piezoelectric element is formed on asurface of a vibrating body formed of constant elastic metal materialand the like. As a vibrating mode of such piezoelectric vibrator, thereare bending vibrating mode, thickness vibrating mode, twisting vibratingmode and longitudinal vibrating mode and the like. The piezoelectricvibrator is used for an oscillator, filter and sensor and the like.

In the conventional piezoelectric vibrator, it becomes difficult tosupport the piezoelectric vibrator due to the miniaturization. Vibrationtends to leak through supporting portion of the piezoelectric vibrator,and the characteristics of the piezoelectric vibrator is deteriorateddue to the vibration leakage. When some displacement or deformationoccurs to the supporting portions of the piezoelectric vibrator by anexternal force, the characteristics of the piezoelectric vibrator varieslargely.

FIG. 57 is an illustrative view showing an example of a conventionalacceleration sensor. The acceleration sensor 1 includes a plate 2. Oneend of the plate 2 is fixed, and a weight 3 is attached to the other endof the plate 2. A piezoelectric elements 4 are formed on both surfacesof the plate 2. When an acceleration is applied in a directionperpendicular to the surface of the plate 2 of the acceleration sensor1, the plate 2 bends as shown in FIG. 58. A voltage corresponding to thebending of plate 2 is generated in the piezoelectric elements 4. Bymeasuring the voltage correspoonding to the bending of plate 2, theacceleration can be detected. The bending of the plate 2 can beincreased by attaching the weight 3, and resulting in improvement of thesensitivity of the acceleration sensor 1.

When such an acceleration sensor is mounted on a car, the impact or thevibration due to unevenness of the road is often stronger than theacceleration of the car. Hence, such an acceleration sensor ofcantilever-construction type is apt to cause misoperation or damage dueto influence of impact attributable to unevenness of the road surface.

It is necessary to use a plurality of acceleration sensors in order todetect accelerations in a plurality of directions.

SUMMARY OF THE INVENTION

It is, therefore, a primary object of the present invention to provide apiezoelectric vibrator which is easy to hold, has reduced vibrationleakage and is less influenced by an external force.

It is the primary object of the present invention to provide anacceleration sensor which can detect a minute acceleration with a highsensitivity and has a high impact resistance by using the abovepiezoelectric vibrator.

It is the another object of the present invention to provide anacceleration sensor capable of detecting accelerations in a plurality ofdirections.

The present invention is directed to a piezoelectric vibrator comprisinga vibrating body, and piezoelectric elements formed on the vibratingbody, wherein the vibrating body vibrates by using the piezoelectriceffect of the piezoelectric elements, and the vibrating body vibrates insuch a manner that expansion and contraction take place simultaneouslyin a part of the vibrating body. The present invention is directed to apiezoelectric vibrator comprising a vibrating body made of piezoelectricmaterial, and electrodes formed on the vibrating body, wherein thevibrating body vibrates by using the piezoelectric effect of thevibrating body, and the vibrating body vibrates in such a manner thatexpansion and contraction take place simultaneously in a part of thevibrating body.

In the above piezoelectric vibrator, it is desirable that the overalllength in a vibrating direction of the vibrating body is almostconstant. Due to the vibration of the vibrating body in such a mannerthat expansion and contraction take place simultaneously in a part ofthe vibrating body, the piezoelectric vibrator whose overall length isalmost constant can be obtained in spite of vibration of the vibratingbody. According to the present invention, the piezoelectric vibrator canbe used in the same manner as the conventional vibrator by using thevibration of the vibrating body. Since the overall size of the vibratingbody is almost constant, the vibrating body can be easily supported atthe portion where has no displacment by the vibration occurs, andvibration leakage can therefore be largely reduced. When the vibratingbody is supported there is no displacement, there are less influences onvibration due to an external force and the like, and the piezoelectricvibrator having stabilized characteristics can be obtained. The presentinvention is directed to an acceleration sensor comprising aplate-shaped vibrating body, opposed piezoelectric elements formed onboth surfaces of the vibrating body, a weight formed at the center ofthe vibrating body, and a supporting means for supporting both ends ofthe vibrating body, wherein the vibrating body vibrates in such a mannerthat longitudinal expansion and contraction take place inversely at bothsides of the center portion of the vibrating body by applying a drivingsignal to the piezoelectric elements.

The present invention is directed to an acceleration sensor comprising aplate-shaped vibrating body made of piezoelectric material, opposedelectrodes formed on both surfaces of the vibrating body, a weightformed at the center of the vibrating body, and a supporting means forsupporting both ends of the vibrating body, wherein the vibrating bodyvibrates in such a manner that longitudinal expansion and contractiontake place inversely at both sides of the center portion of thevibrating body by applying a driving signal to the electrodes.

Since opposed piezoelectric elements are formed on both surfaces of thevibrating body, the vibrating body can be vibrated longitudinally, andan inertia is applied to the vibrating body and the weight. Whenacceleration is given to the vibrating body perpendicular to its surfaceunder such conditions, the vibrating body is bent. By placing the weightat the center of the vibrating body, the bending of the vibrating bodydue to the acceleration is increased. Since both ends of the vibratingbody are supported, impact resistance is increased. Since the vibratingbody vibrates in such a manner that longitudinal expansion andcontraction take place at both sides of the center portion of thevibrating body, displacement is mutually offset, and results in lessvibration leakage to the supporting means.

According to the present invention, the vibrating body bends largelyeven when a minute acceleration is applied to the acceleration sensor.Hence, the voltage generated in the piezoelectric element is increased,and the detection sensitivity can be improved. Since the accelerationsensor has a structure of supporting both ends of the vibrating body,the acceleration sensor has a high impact resistance, and is safe fromdamage due to unevenness of the road even when it is mounted on a car.Since the vibration leakage of the vibrating body is small, stabilizedvibration can be obtained, and results in an improved stabilization ofits characteristics.

The present invention is directed to an acceleration sensor comprising aplate-shaped vibrating body, opposed piezoelectric elements formed onboth surfaces of the vibrating body, and weights formed at bothlongitudinal ends of the vibrating body, wherein the vibrating bodyvibrates in such a manner that longitudinal expansion and contractiontake place inversely at both sides of the center portion of thevibrating body by applying a driving signal to the piezoelectricelements.

The present invention is directed to an acceleration sensor comprising aplate-shaped vibrating body made of piezoelectric material, opposedelectrodes formed on both surfaces of the vibrating body, and weightsformed at both longitudinal ends of the vibrating body, wherein thevibrating body vibrates in such a manner that longitudinal expansion andcontraction take place inversely at both sides of the center portion ofthe vibrating body by applying a driving signal to the electrodes.

In the acceleration sensor, a frame for supporting both longitudinalends of the vibrating body may be formed.

By applying a signal to the piezoelectric elements formed on thesurfaces of the vibrating body, it is possible to vibrate the vibratingbody in a longitudinal direction, and inertia is applied to thevibrating body. When acceleration is applied to the vibrating bodyperpendicular to its surface under such a condition, the vibrating bodyis bent. Since the weights are formed at both longitudinal ends of thevibrating body, the bending of the vibrating body is increased. Sinceboth ends of the vibrating body are supported with the frame, impactresistance is increased. Since the vibrating body vibrates in such amanner that longitudinal expansion and contraction take place inverselyat both sides of the center portion of the vibrating body, displacementis mutually offset, and results in less vibration leakage to the frame.

According to the present invention, the vibrating body bends largelyeven when a minute acceleration is applied to the acceleration sensor.Hence, the voltage generated in the piezoelectric element is increased,and the detection sensitivity can be improved. Since the accelerationsensor has a structure of supporting both ends of the vibrating body bythe frame, the acceleration sensor has a high impact resistance, and issafe from damage due to unevenness of the road even when it is mountedon a car. Since the vibration leakage of the vibrating body is small,stabilized vibration can be obtained, and resulting in a improvedstabilization of its characteristics.

The present invention is directed to an acceleration sensor comprising aprism-shaped vibrating body, and a plurality of piezoelectric elementsarranged peripherally on the side faces of the vibrating body, whereinthe vibrating body vibrates in such a manner that longitudinal expansionand contraction take place inversely at both sides of the center portionof the vibrating body by applying a driving signal to the piezoelectricelements.

The present invention is directed to an acceleration sensor comprising aprism-shaped vibrating body made of piezoelectric material, and aplurality of electrodes arranged peripherally on side faces of thevibrating body, wherein the vibrating body vibrates in such a mannerthat longitudinal expansion and contraction take place inversely at bothsides of the center portion of the vibrating body by applying a drivingsignal to the electrodes.

By applying a driving signal to the piezoelectric elements or electrodesformed on the side faces of the vibrating body, it is possible tovibrate the vibrating body in a longitudinal direction, and inertia isapplied to the vibrating body. When acceleration is applied to theacceleration sensor perpendicular to its side face under such acondition, the vibrating body is bent. Corresponding to bending of thevibrating body, a voltage is generated in the piezoelectric elements.Since the piezoelectric elements are formed peripherally in a pluralityof positions on the side faces of the vibrating body, voltage isgenerated in each piezoelectric element corresponding to theacceleration component in the direction perpendicular to the surface ofeach piezoelectric element.

According to the present invention, since voltage is generated in eachpiezoelectric element corresponding to the acceleration component in thedirection perpendicular to the surface of each piezoelectric element, itis possible to detect the acceleration in every direction perpendicularto the central axis of the vibrating body.

The present invention is directed to an acceleration sensor comprising aplurality of plate-shaped vibrating bodies connected with each other sothat the surfaces of the vibrating bodies are crossed on one centralaxis, and piezoelectric elements are formed on surfaces of a pluralityof vibrating bodies, wherein the vibrating bodies connected with eachother vibrate in such a manner that longitudinal expansion andcontraction take place inversely at both sides of the center portion ofthe vibrating bodies by applying a driving signal to the piezoelectricelements.

The present invention is directed to an acceleration sensor comprising aplurality of plate-shaped vibrating bodies made of piezoelectricmaterial connected with each other so that the surfaces of the vibratingbodies are crossed on one central axis, and electrodes formed onsurfaces of a plurality of vibrating bodies, wherein the vibratingbodies connected with each other vibrate in such a manner thatlongitudinal expansion and contraction take place inversely at bothsides of the center portion of the vibrating bodies by applying adriving signal to the electrodes.

By applying a driving signal to the piezoelectric elements or electrodesformed on surfaces on a plurality of vibrating bodies, it is possible tovibrate the vibrating bodies in a longitudinal direction, and inertia isapplied to the vibrating bodies. When acceleration is given to theacceleration sensor in the direction perpendicular to the central axisof the vibrating bodies under such a condition, the vibrating bodies arebent. Since the vibrating bodies are formed in a plate-shape, largebending of the vibrating bodies can be obtained as compared with theprism-shaped vibrating body. The piezoelectric elements or theelectrodes are formed on the surfaces of the plate-shaped vibratingbodies, and the surfaces of the vibrating bodies are crossed on onecentral axis with each other. Therefore, voltage corresponding to theacceleration component perpendicular to the surface of each vibratingbody is generated in each piezoelectric element or vibrating body formedof piezoelectric material.

According to the present invention, since voltage can be obtained fromevery piezoelectric element corresponding to the acceleration componentperpendicular to the surface of each vibrating body, it is possible todetect the acceleration in every direction perpendicular to the centralaxis of the vibrating body. Since each vibrating body is formed in aplate-shape, large bending corresponding to acceleration can beobtained, and results in large output voltage. Therefore, large outputvoltage can be obtained even when a minute acceleration is given to theacceleration sensor, and the acceleration sensor having high detectingsensitivity can be obtained.

The present invention is directed to an acceleration sensor comprising aplurality of plate-shaped vibrating bodies connected in a folded manner,and piezoelectric elements are formed on surfaces of the vibratingbodies, wherein the vibrating bodies vibrate in such a manner thatlongitudinal expansion and contraction take place inversely at bothsides of the folding portion of the vibrating bodies by applying adriving signal to the piezoelectric elements.

The present invention is directed to an acceleration sensor comprising aplurality of plate-shaped vibrating bodies made of piezoelectricmaterial connected in a folded manner, and electrodes are formed onsurfaces of the vibrating bodies, wherein the vibrating bodies vibratein such a manner that longitudinal expansion and contraction take placeinversely at both sides of the folding portion of the vibrating bodiesby applying a driving signal to the electrodes.

By applying a driving signal to the piezoelectric elements or theelectrodes formed on the surfaces of the vibrating bodies, it ispossible to vibrate the vibrating body in a longitudinal direction, andinertia is given to the vibrating bodies. When acceleration is given tothe acceleration sensor in the direction perpendicular to the centralaxis of either vibrating body under such conditions, the vibrating bodybends. Since the vibrating body is formed in a plate-shape, largebending of the vibrating body can be obtained as compared with theprism-shaped vibrating body. The piezoelectric elements or electrodesare formed on the surfaces of the plate-shaped vibrating bodies, and thevibrating bodies are connected in a folded manner. Hence, voltagecorresponding to the acceleration component perpendicular to eachvibrating body is generated in the piezoelectric element or vibratingbody formed of piezoelectric material.

According to the present invention, since voltage can be obtained fromeach piezoelectric element or electrode corresponding to theacceleration component perpendicular to the surface of each vibratingbody, it is possible to detect the acceleration component in eachdirection perpendicular to the surface of the vibrating body. Since eachvibrating body is formed in a plate-shape, large bending correspondingto acceleration can be obtained, and results in a large output voltage.Therefore, large output voltage can be obtained even when a minuteacceleration is given to the acceleration sensor, and the accelerationsensor having high detecting sensitivity can be obtained.

The above and further objects, features, aspects and advantages of theinvention will be more fully apparent from the following detaileddescription with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view showing an embodiment of the piezoelectricvibrator of the invention.

FIG. 2 is a sectional view showing a piezoelectric vibrator shown inFIG. 1.

FIG. 3 is a circuit diagram for driving a piezoelectric vibrator shownin FIG. 1.

FIGS. 4(A)-4(E) are illustrative views showing a vibrating state of thepiezoelectric vibrator shown in FIG. 1.

FIG. 5 is a graph showing a resonance characteristics of thepiezoelectric vibrator shown in FIG. 1.

FIG. 6 is a perspective view showing a state when the resonancefrequency of the piezoelectric vibrator shown in FIG. 1 is adjusted.

FIG. 7 is an illustrative view showing a modified example of thepiezoelectric vibrator shown in FIG. 1 and the circuit for driving it.

FIG. 8 is an illustrative view showing another embodiment of apiezoelectric vibrator of the invention.

FIG. 9 is a perspective view showing still another embodiment of apiezoelectric vibrator of the invention.

FIG. 10 is an illustrative view showing a vibrating state of thepiezoelectric vibrator shown in FIG. 9.

FIG. 11 is a sectional view showing a further embodiment of thepiezoelectric vibrator of the invention.

FIG. 12 is a plan view showing a first embodiment of an accelerationsensor of the invention.

FIG. 13 is a sectional view showing an acceleration sensor shown in FIG.12.

FIG. 14 is a circuit diagram showing a circuit for using theacceleration sensor shown in FIG. 12.

FIG. 15 is an illustrative view showing a state of the vibrating bodywhen the acceleration is given to the acceleration sensor shown in FIG.12.

FIG. 16 is a sectional view showing a second embodiment of anacceleration sensor of the invention.

FIG. 17 is a plan view showing a third embodiment of an accelerationsensor of the invention.

FIG. 18 is a sectional view showing an acceleration sensor shown in FIG.17.

FIG. 19 is a plan view showing a state of the acceleration sensor whenacceleration is applied to the acceleration sensor shown in FIG. 17.

FIG. 20 is a sectional illustrative view showing an acceleration sensorshown in FIG. 19.

FIG. 21 is a sectional illustrative view showing a fourth embodiment ofan acceleration sensor of the invention.

FIG. 22 is a sectional illustrative view showing a fifth embodiment ofan acceleration sensor of the invention.

FIG. 23 is a sectional view showing a sixth embodiment of anacceleration sensor of the invention.

FIG. 24 is a sectional illustrative view showing a seventh embodiment ofan acceleration sensor of the invention.

FIG. 25 is a plan view showing an eighth embodiment of an accelerationsensor of the invention.

FIG. 26 is a sectional view showing an acceleration sensor shown in FIG.25 which is cut across one opposite side.

FIG. 27 is a sectional view showing an acceleration sensor shown in FIG.25 which is cut across the other opposite side.

FIG. 28 is a circuit diagram showing a driving circuit for vibrating anacceleration sensor shown in FIG. 25.

FIG. 29 is an illustrative view showing a state that acceleration isgiven to an acceleration sensor shown in FIG. 25.

FIG. 30 is a circuit diagram showing a detecting circuit for measuringan output voltage of an acceleration sensor shown in FIG. 25.

FIG. 31 is a plan view showing a ninth embodiment of an accelerationsensor of the invention.

FIG. 32 is a sectional view showing an acceleration sensor shown in FIG.31 which is cut across one opposite side.

FIG. 33 is a sectional view showing an acceleration sensor shown in FIG.31 which is cut across the other opposite side.

FIG. 34 is a circuit diagram showing a driving circuit and a detectingcircuit for an acceleration sensor shown in FIG. 31.

FIG. 35 is a sectional view showing a tenth embodiment of anacceleration sensor of the invention.

FIG. 36 is a sectional view showing an acceleration sensor shown in FIG.35 which is cut across the other side.

FIG. 37 is a perspective view showing an eleventh embodiment of anacceleration sensor of the invention.

FIG. 38 is a sectional view showing an acceleration sensor shown in FIG.37 taken along the line XXXVIII--XXXVIII.

FIG. 39 is a sectional view showing an acceleration sensor shown in FIG.37 taken along the line XXXIX--XXXIX.

FIG. 40 is a plan view showing a state in which an acceleration sensorshown in FIG. 37 is held by the holding member.

FIG. 41 is a circuit diagram showing a circuit for an accelerationsensor shown in FIG. 37 when it is used.

FIG. 42 is an illustrative view showing a state that acceleration isapplied to an acceleration sensor shown in FIG. 37 in the directionperpendicular to the surface of the first vibrating body.

FIG. 43 is an illustrative view showing a state that acceleration isapplied to an acceleration sensor shown in FIG. 37 in the directionperpendicular to the surface of the second vibrating body.

FIG. 44 is a front view showing a twelfth embodiment of an accelerationsensor of the invention.

FIG. 45 is a side view showing an acceleration sensor shown in FIG. 44.

FIG. 46 is a sectional view showing a thirteenth embodiment of anacceleration sensor of the invention.

FIG. 47 is a sectional view showing an acceleration sensor shown in FIG.46 which is cut across the other side.

FIG. 48 is a perspective view showing a fourteenth embodiment of anacceleration sensor of the invention.

FIG. 49 is a sectional view showing an acceleration sensor shown in FIG.48.

FIG. 50 is a circuit diagram showing a circuit for an accelerationsensor shown in FIG. 48 when it is used.

FIG. 51 is an illustrative view showing a vibrating state of anacceleration sensor shown in FIG. 48 at a given time.

FIG. 52 is an illustrative view showing a vibrating state of anacceleration sensor shown in FIG. 48 at another given time.

FIG. 53 is an illustrative view showing a state that acceleration isapplied to an acceleration sensor shown in FIG. 48 in the directionperpendicular to the surface of the first vibrating body.

FIG. 54 is an illustrative view showing a state that acceleration isapplied to an acceleration sensor shown in FIG. 48 in the directionperpendicular to the surface of the second vibrating body.

FIG. 55 is an illustrative view showing a fifteenth embodiment of anacceleration sensor of the invention.

FIG. 56 is a sectional view showing a sixteenth embodiment of anacceleration sensor of the invention.

FIG. 57 is a illustrative view showing an example of a conventionalacceleration sensor which is a background of the invention.

FIG. 58 is an illustrative view showing a state that acceleration isgiven to an acceleration sensor shown in FIG. 57.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is a perspective view showing an embodiment of the presentinvention, and FIG. 2 is a sectional view thereof. A piezoelectricvibrator 10 comprises a plate-shaped vibrating body 12. The vibratingbody 12 is made of, for example, a constant elastic material such aselinvar, iron-nickel alloy, quartz, glass, crystal and ceramics. Thevibrating body 12 is supported at both ends.

Piezoelectric elements 14a, 14b, 14c and 14d are formed on oppositesurfaces of the vibrating body 12. The piezoelectric elements 14a and14b are formed on opposite surfaces of the vibrating body 12 at one sideportion adjacent the longitudinal center portion of the vibrating body12. The piezoelectric elements 14c and 14d are formed on oppositesurfaces of the vibrating body 12 at the other side portion adjacent thelongitudinal center portion of the vibrating body 12 . The piezoelectricelement 14a includes a piezoelectric plate 16a made of, for example,piezoelectric ceramics . Electrodes 18a and 20a are formed on bothsurfaces of the piezoelectric plate 16a. One electrode 20a of thepiezoelectric element 14a is bonded to the vibrating body 12. Similarly,the piezoelectric elements 14b, 14c and 14d include piezoelectric plates16b, 16c and 16d. On both surfaces of the piezoelectric plates 16b, 16cand 16d, electrodes 18b, 20b, electrodes 18c, 20c and electrodes 18d,20d are formed. The electrodes 20b, 20c, 20d of the piezoelectricelements 14b, 14c, 14d are bonded to the vibrating body 12. In thisembodiment, the piezoelectric plates 16a and 16b are polarized fromoutside toward the vibrating body 12 side, and piezoelectric plates 16cand 16d are polarized from the vibrating plate 12 side toward outside.

For vibrating the piezoelectric vibrator 10, an oscillation circuit 22is connected to the piezoelectric elements 14a-14d as shown in FIG. 3.Driving signals having the same phase are applied to the piezoelectricelements 14a-14d from the oscillation circuit 22. The piezoelectricelements 14a and 14b are formed to be opposite to each other with thevibrating body 12 between them, and the piezoelectric elements 14c and14d are formed to be opposite to each other with the vibrating body 12between them. Hence, when driving signals are applied to thepiezoelectric elements 14a-14d, the vibrating body 12 vibrates in alongitudinal direction. Since the piezoelectric elements 14a, 14b andpiezoelectric elements 14c, 14d are polarized in the inverse situation,as shown in FIG. 4(A)-FIG. 4(E), when one side of the vibrating body 12adjacent the longitudinal center portion expands, the other side of thevibrating body 12 contracts. When one side of the vibrating body 12adjacent the longitudinal center portion contracts, the other side ofthe vibrating body 12 expands. Therefore, even when the vibrating body12 is vibrating, both end portions of the vibrating body 12 are notdisplaced. When the length of the vibrating body 12 is taken as L, itsdensity is taken as P, and the Young's modulus is taken as E, theresonance frequency f is represented by the following formula. ##EQU1##

The frequency characteristics of phase and impedance of piezoelectricvibrator 10 are shown in FIG. 5. As shown from FIG. 5, the piezoelectricvibrator 10 has fine resonance characteristics, and is well usable as anresonator. Even when the vibrating body 12 is vibrating, thedisplacement of the both end portions of vibrating body 12 is offsetsince the expanding portion and the contracting portion exist in thevibrating body 12. Hence, the overall length of the vibrating body 12 isalmost constant, and the vibration leakage from the supporting portionis reduced by supporting the vibrating body 12 at both ends. Even if anexternal force is applied to the supporting portions, there is lessinfluences on the vibration of the vibrating body 12 since thesupporting portions have no displacement.

As shown from the above formula, in the piezoelectric vibrator 10, theresonance frequency is adjustable by adjusting the overall length of thevibrating body 12. For example, when both ends of the vibrating body 12is cut to make the overall length of the vibrating body 12 smaller, itis possible to increase the resonance frequency. As shown from FIG. 6,if any groove 30 extending laterally is formed at the central portion ofthe vibrating body 12, it is possible to increase the surface length ofthe vibrating body 12 and decrease the resonance frequency.

In the above embodiment, the piezoelectric elements 14a, 14b and thepiezoelectric elements 14c, 14d are polarized in the inverse situation,it is possible to polarize all piezoelectric elements 14a-14d in thesame situation. That is, the piezoelectric elements 14a-14d may bepolarized from the outside surface toward the vibrating body 12 side,and the piezoelectric elements 14a-14d may be polarized from thevibrating body 12 side toward the outside surface. In this case, byapplying driving signals having inverse phases to the piezoelectricelements 14a, 14b and the piezoelectric elements 14c, 14d, it ispossible to vibrate the vibrating body 12 in such a manner thatlongitudinal expansion and contraction take place inversely on bothsides of the center portion of the vibrating body 12.

As shown in FIG. 7, two piezoelectric elements 32 and 34 may be formedon both surfaces of the vibrating body 12. The piezoelectric element 32includes a piezoelectric plate 36. Two electrodes 38a and 38b are formedon one surface of the piezoelectric plate 36, and an electrode 40 isformed on the entire other surface of the piezoelectric plate 36. Theelectrode 40 is bonded to the vibrating body 12. Similarly, thepiezoelectric element 34 includes a piezoelectric plate 42, andelectrodes 44a, 44b and an electrode 46 are formed on both surfaces ofthe piezoelectric plate 42. The electrode 46 is bonded to the vibratingbody 12. In the piezoelectric elements 32 and 34, the piezoelectricplates 36 and 42 are polarized, for example, from the outside surfacetoward the vibrating body 12 side. The driving signals are inverted inpolarity in a circuit of FIG. 7, and the driving signals applied to theelectrodes 38a, 44a and the driving signals applied to the electrodes38b, 44b have inverse phase. Needless to say, when such a circuit isused, the piezoelectric plates 36 and 42 may be polarized from the thevibrating body 12 side the toward outside surface. In the piezoelectricvibrator 10 shown in the above embodiments, it is not always necessaryto support the vibrating body 12 at both ends, and, for example, thevibrating body 12 may be supported at the inward portions approximately1/4 from both ends. There is no displacement at this point, and it ispossible to prevent vibration leakage from the supporting portions.

The number of piezoelectric elements is not necessarily four and, asshown in FIG. 8, six piezoelectric elements 50a, 50b, 50c, 50d, 50e and50f may be formed. The piezoelectric elements 50c and 50d are formed tobe opposite to each other at the center portion of the vibrating body12, and the piezoelectric elements 50a, 50b and the piezoelectricelements 50e, 50f are formed to be opposite to each other at both sideportions of the piezoelectric elements 50c, 50d. The length of thepiezoelectric elements 50c, 50d is adjusted to be approximately twicethe length of the piezoelectric elements 50a, 50b, 50e, 50f in thevibrating direction. In the piezoelectric vibrator 10, the piezoelectricelements 50a, 50b, 50e, 50f are polarized from the outside surfacetoward the vibrating body 12 side, and the piezoelectric elements 50c,50d are polarized from the vibrating body 12 side toward the outsidesurface. Needless to say, the polarizing direction of the piezoelectricelements 50a-50f may be the inverse situation.

When driving signals having the same phase are applied to thepiezoelectric elements 50a-50f, the vibrating body 12 vibrates in such amanner that longitudinal expansion and contraction take place inverselyat both portions of approximately 1/4 from both ends as shown witharrows in FIG. 8. In such a piezoelectric vibrator 10, it is possible tosupport the vibrating body 12 at both ends or at the center portion, andit is possible to prevent vibration leakage. In the piezoelectricvibrator 10 in FIG. 8, as compared with the piezoelectric vibrator shownin FIG. 1, reaction resulting from shifting of gravity can be offset. Itis possible to polarize all of the piezoelectric elements 50a-50f in thesame situation and make the driving signals be applied to thepiezoelectric elements 50a, 50b, 50e, 50f and the piezoelectric elements50c, 50d in inverse phase. In the above embodiments, though therectangular plate-shaped vibrating body 12 is used, a prism-shapedvibrating body or cylindrical vibrating body may be used, andpiezoelectric elements may be formed to be opposite to each other with avibrating body between them. As shown in FIG. 9, it is possible to use adisk-shaped vibrating body 12. In this case, the piezoelectric elements14a-14d are formed in a concentric circle-shape. The piezoelectricelements 14a, 14b are formed to be opposite to each other with thevibrating body 12 between them, and the piezoelectric elements 14c, 14dare formed to be opposite to each other with the vibrating body 12between them. The piezoelectric vibrator 10 vibrates in a diametricaldirection as shown in FIG. 10. The vibrating body 12 vibrates in such amanner that expansion and contraction take place both portions of a halfcircle as the center. Hence, no displacement occurs in the outer circleof the vibrating body 12, and the vibrating body 12 can be supported atthe outer circle. Thus, many shapes of the vibrating body 12 may be usedsuch as plate-shape or prism-shape.

In the above embodiments, as shown in FIG. 11, the vibrating body 12 maybe made of piezoelectric ceramics. In this case, electrodes 60a, 60b,60c and 60d are formed at the same position as the piezoelectricelements 14a-14d.

By applying driving signals having inverse phase to the electrodes 60a,60b and the electrodes 60c, 60d, it is possible to vibrate the vibratingbody 12 in such a manner that expansion and contraction take placesimultaneously.

The vibrating body 12 may be polarized partially in an inversedirection. For example, a part which is put between the electrodes 60aand 60b is polarized from the electrode 60a side toward the electrode60b side, and a part which is put between the electrodes 60c and 60d ispolarized from the electrode 60d side toward the electrode 60c side. Inthis case, by applying driving signals having the same phase to theelectrodes 60a, 60b and the electrodes 60c, 60d, it is possible tovibrate the vibrating body 12 in such a manner that expansion andcontraction take place simultaneously.

Similarly, in the case of a piezoelectric vibrator having the shapes asshown in FIG. 6, FIG. 8 and FIG. 9, the vibrating body may be made ofpiezoelectric ceramics, and electrodes may be formed instead ofpiezoelectric elements at the same places.

In the piezoelectric vibrator of the present invention, the vibratingbody 12 can be manufactured by micromachining, etching or press-molding,and a piezoelectric vibrator having good productivity can be obtained.

By using the piezoelectric vibrator 10, an acceleration sensor can bemanufactured as shown in FIG. 12 and FIG. 13. In this embodiment, thepiezoelectric vibrator shown in FIG. 1 and FIG. 2 is used. In theacceleration sensor 100, weights 102 are attached to the center portionof the vibrating body 12. Piezoelectric elements 14a and 14b are formedon the opposite surfaces of the vibrating body 12 at one side portion ofthe weights 102. Piezoelectric elements 14c and 14d are formed on theopposite surfaces of the vibrating body 12 at the other side portion ofthe weights 102.

The vibrating body 12 is supported at both ends by a frame 104 assupporting means. The frame 104 is formed, for example, in a square loopshape, and the vibrating body 12 is arranged at the center of the frame104. The vibrating body 12 may be supported by other means if it isproper for supporting the vibrating body 12.

When the acceleration sensor 100 of FIG. 13 is used, as shown in FIG.14, an oscillation circuit 110 is connected to piezoelectric elements14a, 14b and the piezoelectric elements 14c, 14d via resistors 108a,108b, 108c and 108d. By the driving signal from the oscillation circuit110, as indicated with solid line arrow in FIG. 12, when one side of thevibrating body 12 expands, the other side of the vibrating body 12contracts with the weights 102 as a center. When one side of thevibrating body 12 contracts, the other side of the vibrating body 12expands as indicated by the one dot chain line arrow in FIG. 12. In sucha way, the vibrating body 12 vibrates in a longitudinal direction.Hence, the displacement of both sides of the vibrating body 12 isoffset, and both ends of the vibrating body 12 are not displaced, andresults in less vibration leakage from the vibrating body 12 to theframe 104. Therefore, stabilized vibration can be obtained.

By vibrating the vibrating body 12, inertia is applied to the vibratingbody 12 and the weights 102. When acceleration is applied to thevibrating body 12 perpendicular to its surface, the vibrating body 12 isbent as shown in FIG. 15. By the bending of the vibrating body 12,voltages are generated in the piezoelectric elements 14a, 14b and thepiezoelectric elements 14c, 14d. Therefore, acceleration can be detectedby measuring the voltages.

For detecting the acceleration, the voltages generated in thepiezoelectric elements 14a, 14b and the piezoelectric elements 14c, 14dare measured. For this purpose, as shown in FIG. 14, the piezoelectricelements 14a, 14b are connected to a differential circuit 112, and thepiezoelectric elements 14c, 14d are connected to the differentialcircuit 114. However, it is not necessary to use two differentialcircuits, and either differential circuit 112 or 114 may be connected tothe piezoelectric elements. By connecting the opposed piezoelectricelements 14a, 14b to the differential circuit 112, the driving signalsare offset and only the output signals corresponding to acceleration canbe measured. Since the piezoelectric elements 14a and 14b are polarizedfrom the outside surface toward the inside, voltages having inversephase are generated according to the bending of the vibrating body 12.Hence, a large output can be obtained from the differential circuit 112when the difference of the output voltages of the piezoelectric elements14a, 14b is measured, and results in high sensitivity. It is possible toincrease the bending of the vibrating body 12 due to acceleration withthe weights 102, and if the weights 102 are adjusted according to thedetection range of acceleration, further improved sensitivity can beobtained.

In the acceleration sensor 100, since vibration is applied to theweights 102, the acceleration sensor 100 has high responsibility andhigh sensitivity. Since the vibrating body 12 is supported at both ends,the acceleration sensor 100 having high impact resistance and less indamage can be obtained. Hence, when the acceleration sensor 100 ismounted on a car, the acceleration sensor 100 has no damage due tounevenness of the road, and can detect acceleration by the car with highsensitivity. The vibrating body 12 can be made by stamping or etchingeasily and at a low cost.

In the above embodiment, though the output voltages of piezoelectricelements 14a, 14b or the piezoelectric elements 14c, 14d are applied tothe differential circuit, the difference between the output voltages ofthe piezoelectric elements 14a, 14b which are formed at the same surfaceor the output voltages of piezoelectric elements 14c, 14d may bemeasured. The four piezoelectric elements 14a, 14b, 14c, 14d may beconnected to form a bridge circuit or the like for detectingacceleration.

Though the piezoelectric elements 14a, 14b and the piezoelectricelements 14c, 14d are polarized in an inverse situation, thesepiezoelectric elements may be polarized in the same situation. In thiscase, driving signals having inverse phase are applied to thepiezoelectric elements 14a, 14b and the piezoelectric elements 14c, 14d.In this way, the vibration described in the above embodiment can beobtained. When this driving method is used, the voltages generatedbetween the piezoelectric elements 14a and 14c on the same surface havethe same phase, as well as the voltages generated between thepiezoelectric elements 14b, 14d. Hence, when the output signals of thepiezoelectric elements on the same surface are used for measuring, alarge output can be obtained by using a cumulative circuit. Since thedriving signals to be applied to the piezoelectric elements have inversephases, these signals are offset by means of the cumulative circuit.

Further, the number of the piezoelectric elements is not necessarilyfour and, for example, only opposed two piezoelectric elements 14a and14b may be formed. As such, vibration as described above can be obtainedif a pair of opposed piezoelectric elements are formed on both surfacesof the vibrating body 12.

Needless to say, it is possible to make an acceleration sensor 100 byusing the vibrating body shown in FIG. 11. In this case, weights 102 areformed at the center portion of the vibrating body 12 made ofpiezoelectric material as shown in FIG. 16, and electrodes 60a, 60b,60c. 60d are formed on both surfaces of the vibrating body 12. Thevibrating body 12 vibrates in such a manner that longitudinal expansionand contraction take place simultaneously by applying driving signalshaving inverse phase to the electrodes 60a, 60b and the electrodes 60c,60d. When acceleration is applied to the acceleration sensor 100perpendicular to the surface of the vibrating body 12, the vibratingbody 12 is bent, and output signals corresponding to the accelerationcan be obtained from the electrodes 60a-60d.

The vibrating body 12 may be polarized partially in an inversedirection. For example, a part which is put between the electrodes 60aand 60b is polarized from the electrode 60a side toward the electrode60b side, and a part which is put between the electrodes 60c and 60d ispolarized from the electrode 60d side toward the electrode 60c side. Inthis case, by applying driving signals having the same phase to theelectrodes 60a, 60b and the electrodes 60c, 60d, it is possible tovibrate the vibrating body 12 in such a manner that expansion andcontraction take place simultaneously.

Weights 120 may be attached to both longitudinal ends of the vibratingbody 12 as shown in FIG. 17 and FIG. 18. The weights 120 are formed tobe opposite to both faces of, for example, a frame 104. The frame 104 issupported at the supporting portions 122a, 122b which corresponds to thelongitudinal center of the vibrating body 12. That is, these supportingportions 122a, 122b are positioned at the center of the parts of frame104 which is parallel to the vibrating body 12.

In this acceleration sensor 100 too, the vibrating body 12 can bevibrated by using the circuit shown in FIG. 14. When acceleration isapplied to the acceleration sensor 100 perpendicular to the surface ofthe vibrating body 12, the vibrating body 12 is bent as shown in FIG. 19and FIG. 20. When the vibrating body 12 bends, the frame 104 is deformedwith the supporting portions 122a, 122b as the center by the mass of theweights 120 attached to both longitudinal ends of the vibrating body 12.The bending of the vibrating body 12 due to acceleration is increased bythe deformation of the frame. This bending results with vibration of thevibrating body 12, and resulting in variation of the resonancecharacteristics. By measuring the variation of resonancecharacteristics, acceleration can be detected. In order to detect theacceleration, the difference between the output signals of thepiezoelectric elements 14a, 14b or the difference between the outputsignals of the piezoelectric elements 14c, 14d is measured like theacceleration sensor shown in FIG. 12 and FIG. 13.

Such an acceleration sensor 100 has high responsibility and highsensitivity.

As shown in FIG. 21, piezoelectric elements 62a, 62b, 62c, 62d fordetecting may be formed besides the piezoelectric elements 14a, 14b,14c, 14d for driving. In the embodiment shown in FIG. 21, thepiezoelectric elements 62a-62d for detecting are formed on the frame 104side of the vibrating body 12. Acceleration applied to the accelerationsensor 100 can be detected by measuring the voltages generated in thepiezoelectric elements 62a-62d for detecting according to the bending ofthe vibrating body 12 due to the acceleration.

As shown in FIG. 22, the piezoelectric elements 14a, 14c for driving maybe formed on one surface of the vibrating body 12, and a piezoelectricelement 64 for detecting may be formed on the other surface of thevibrating body 12. In this case, the piezoelectric element 64 fordetecting is formed to be symmetric with respect to the longitudinalcenter of the vibrating body 12. In the acceleration sensor 100, anoscillation circuit 110 is connected to the piezoelectric elements 14a,14c for driving and the vibrating body 12 is vibrated. When thevibrating body 12 of the acceleration sensor 100 does not bend, thevoltage generated in the piezoelectric element 64 for detecting isoffset because expansion and contraction take place inversely at bothsides of the central portion of the piezoelectric element 64 fordetecting. When, the vibrating body 12 bends by the acceleration,difference of bending occures between both side portions of the centerof the piezoelectric element 64 for detecting, and output voltage whichis not offset is obtained. Hence, the acceleration can be detected bymeasuring the output voltage of the piezoelectric element 64 fordetecting.

In the above embodiments, though the vibrating body or the frame made ofmetallic material or the like is used, these may be made ofpiezoelectric ceramics as shown in FIG. 23. In this case, electrodes60a-60d are formed instead of the piezoelectric elements on thevibrating body like the acceleration sensor shown in FIG. 16. Byapplying driving signals having inverse phase to the electrodes 60a, 60band the electrodes 60c, 60d, it is possible to vibrate the vibratingbody in such a manner that longitudinal expansion and contraction takeplace simultaneously. By measuring the output signals from theelectrodes, it is possible to detect the acceleration.

The vibrating body 12 may be polarized partially in an inversedirection. For example, a part which is put between the electrodes 60aand 60b is polarized from the electrode 60a side toward the electrode60b side, and a part which is put between the electrodes 60c and 60d ispolarized from the electrode 60d side toward the electrode 60c side. Inthis case, by applying driving signals having the same phase to theelectrodes 60a, 60b and the electrodes 60c, 60d, it is possible tovibrate the vibrating body 12 in such a manner that expansion andcontraction take place simultaneously.

Similarly, in the case of an acceleration sensor having a shape as shownin FIG. 21 and FIG. 22, the vibrating body may be made of apiezoelectric ceramics and electrodes may be formed instead of thepiezoelectric elements.

The vibrating body 12 is not always necessarily fixed to the frame, andmay be a cantilever structure as shown in FIG. 24. In this case, aweight 120 is attached to one longitudinal end of the vibrating body 12.In such an acceleration sensor 100, the vibrating body 12 is bent byacceleration, and an output corresponding to the bending can beobtained.

FIG. 25 is a plan view showing an acceleration sensor which can detectacceleration in a plurality of directions. An acceleration sensor 100includes, for example, a vibrating body 12 formed in a regularrectangular prism shape. At one longitudinal end side of the vibratingbody 12, piezoelectric elements 14a, 14b for driving are formed on theopposite surfaces of the vibrating body 12 as shown in FIG. 26. At theother longitudinal end side of the vibrating body 12, the otherpiezoelectric elements 14c, 14d for driving are formed on the surfaceson which the piezoelectric elements 14a, 14b for driving are formed. Inthe piezoelectric elements 14a-14d for driving, the piezoelectric plates16a, 16b are polarized from an outside surface toward the vibrating body12 side, and the piezoelectric plates 16c, 16d are polarized from thevibrating body 12 side toward the outside surface.

Piezoelectric elements 66a, 66b for detecting are formed on the surfaceson which the piezoelectric elements 14a, 14b for driving are formed. Thepiezoelectric elements 66a, 66b for detecting are formed adjacent to thepiezoelectric elements 14a, 14b for driving and formed at one end sideof the vibrating body 12. On the surfaces on which the piezoelectricelements 66a, 66b for detecting are not formed, the other piezoelectricelements 66c, 66d for detecting are formed as shown in FIG. 27. Thepiezoelectric elements 66c, 66d for detecting are formed at onelongitudinal end side of the vibrating body 12.

The piezoelectric elements 66a, 66b, 66c, 66d for detecting includepiezoelectric plates 68a, 68b, 68c, 68d. On both faces of thepiezoelectric plates 68a, 68b, 68c, 68d, electrodes 70a, 72a, electrodes70b, 72b, electrodes 70c, 72c and electrodes 70d, 72d are formedrespectively. The electrodes 72a, 72b, 72c, 72d on one surface of thesepiezoelectric plates 66a, 66b, 66c, 66d for detecting are bonded to theside faces of the vibrating body 12. In the piezoelectric elements 66a,66b, 66c, 66d, the piezoelectric plates 68a, 68b, 68c, 68d arepolarized, for example, from the outside surface toward the vibratingbody 12 side.

In the acceleration sensor 100, for example, one end of the vibratingbody 12 is supported, and a weight 120 is attached to the other end ofthe vibrating body 12. Hence, in this embodiment, the vibrating body 12has a cantilever structure. When the acceleration sensor 100 is used, anoscillation circuit 110 is connected to the piezoelectric elements14a-14d for driving as shown in FIG. 28. By the oscillation circuit 110,the vibrating body 12 vibrates in a longitudinal direction as indicatedwith arrows in FIG. 25.

When acceleration is applied to the acceleration sensor 100, forexample, perpendicular to the surfaces of the piezoelectric elements66a, 66b for detecting, the vibrating body 12 bends in the directionperpendicular to the surfaces of the piezoelectric elements 66a, 66b fordetecting as shown in FIG. 29. Bending of the vibrating body 12interferes with the vibration of the vibrating body 12, and results invariation of the resonance characteristics. By measuring the variationof resonance characteristics, acceleration can be detected. In order todetect the acceleration, the voltages generated in the piezoelectricelements 66a, 66b for detecting are measured. In order to detect theacceleration perpendicular to the surfaces of the piezoelectric elements66c, 66d for detecting, the voltages generating in the piezoelectricelements 66c, 66d for detecting are measured.

For detecting the acceleration, as shown in FIG. 30, the piezoelectricelements 66a, 66b for detecting are connected to the differentialcircuit 112, and the other piezoelectric elements 66c, 66d for detectingare connected to the other differential circuit 114. Since thepiezoelectric elements 66a-66d are polarized from the outside surfacetoward the vibrating body 12 side, the voltages having the samemagnitude and the same phase are generated in the piezoelectric elements66a-66d when no acceleration is applied to the acceleration senser 100.Therefore, the outputs from the differential circuit 112 and 114 arezero. When acceleration is applied to the acceleration sensor 100 andthe vibrating body 12 is bent, voltages having the inverse phase aregenerated in the opposed piezoelectric elements. Hence, by measuring thedifference between output voltages of the opposed piezoelectric elements66a, 66b for detecting, a large output signal can be obtained from thedifferential circuit 112. Therefore, the acceleration in the directionperpendicular to the surfaces of the piezoelectric elements 66a, 66b fordetecting can be detected with a high sensitivity. Similarly, bymeasuring the difference between the output voltages of thepiezoelectric elements 66c, 66d for detecting, the acceleration in thedirection perpendicular to the surfaces of the piezoelectric elements66c, 66d for detecting can be detected with a high sensitivity.

When the acceleration not perpendicular to the surfaces of thepiezoelectric elements 66a-66d is applied to the accelerlation sensor,the vibrating body 12 bends in the direction along which theacceleration is applied. The voltages corresponding to the bending ofthe vibrating body 12 is generated in the piezoelectric elements 66a-66dfor detecting. That is, voltages generated in the piezoelectric elements66a-66d for detecting corresponds to the acceleration components in thedirection perpendicular to the surfaces of the piezoelectric elements66a-66d. Therefore, the acceleration in all directions perpendicular tothe center axis can be detected by measuring the output signals from thedifferential circuits 112 and 114.

The piezoelectric elements 66a-66d for detecting are not necessarilyessential, and the piezoelectric elements 14a-14d for driving may beused for detecting. In this case, as shown in FIG. 31, FIG. 32 and FIG.33, the piezoelectric elements 14a, 14b for driving and thepiezoelectric elements 14c, 14d for driving are formed on differentopposite surfaces of the vibrating body 12. The piezoelectric elements14a, 14b for driving are formed at one end side of the vibrating body12, and the piezoelectric elements 14c, 14d for driving are formed atthe other end side of the vibrating body 12. In the acceleration sensor100, the piezoelectric elements 14a, 14b for driving and thepiezoelectric elements 14c, 14d for driving are polarized in the inversedirection. As shown in FIG. 34, an oscillation circuit 110 is connectedto the piezoelectric elements 14a-14d for driving via the resistors108a, 108b, 108c, 108d. By the signal from the oscillation circuit 110,the vibrating body 12 vibrates in a longitudinal direction. By applyingthe signals having the same phase to the piezoelectric elements 14a-14dfor driving, the vibrating body 12 vibrates in such a manner thatlongitudinal expansion and contraction take place inversely on bothsides of the center portion of the vibrating body 12. The piezoelectricelements 14a, 14b for driving are connected to the input terminal of thedifferential circuit 112, and the piezoelectric elements 14c, 14d fordriving are connected to the input terminal of the differential circuit114. When acceleration is applied to the acceleration sensor 100 and thevibrating body 12 is bent, a voltage is generated in each piezoelectricelements 14a-14d. By measuring the differences between these voltages bythe differential circuits 112 and 114, the acceleration applied to theacceleration sensor 100 can be detected. The driving signals applied tothe piezoelectric elements 14a-14d are offset in the differentialcircuits 112 and 114. Therefore, only the output signals correspondingto the acceleration are obtained from the output terminals of thedifferential circuits 112 and 114.

In the above embodiment, the vibrating body 12 is not necessarily of thecantilever structure, and may be the structure that both ends of thevibrating body 12 are supported. In this case, for example, thevibrating body 12 is supported with a frame or the like. Thus, even ifthe vibrating body 12 has a structure that the vibrating body 12 issupported at both ends, vibration leakage is small because both endportions of the vibrating body 12 are not displaced. Therefore, anacceleration sensor having excellent characteristics can be obtained. Inthe acceleration sensor having a structure that the vibrating body 12 issupported at both ends, weights may be formed at both ends of thevibrating body 12. In this way, when the vibrating body 12 bends,bending can be increased by the mass of the weight, and the accelerationsensor having a high sensitivity can be obtained.

In the above embodiments, though the piezoelectric elements 14a, 14b andthe piezoelectric elements 14c, 14d are polarized in the inversedirection, all piezoelectric elements 14a-14d may be polarized in thesame direction. That is, the piezoelectric elements 14a-14d may bepolarized from the outside surface toward the vibrating body 12 side,and may be polarized from the vibrating body 12 side toward the outsidesurface. In such a case, the driving signals applied to thepiezoelectric elements 14a, 14b and the driving signals applied to thepiezoelectric elements 14c, 14d have inverse phase. In this way, thevibrating body 12 can be vibrated in such a manner that longitudinalexpansion and contraction take place inversely at both sides of thecenter portion of the vibrating body 12.

As to the shape of the vibrating body 12, it may be any of a pentagonalprism shape such as hexagonal prism shape or octagonal prism shape orcolumner shape. With any of such columner shape or prism shape,acceleration can be detected if the piezoelectric elements for drivingare formed at opposite side faces and the piezoelectric elements areformed at a plurality of positions along its periphery.

As shown in FIG. 35 and FIG. 36, the vibrating body may be made of apiezoelectric ceramics. In this case, electrodes 60a, 60b, 60c, 60d fordriving and electrodes 124a, 124b, 124c, 124d for detecting are formedinstead of the piezoelectric elements. The vibrating body 12 can bevibrated by applying the driving signals having inverse phase to theelectrodes 60a, 60b for driving and the electrodes 60c, 60d for driving.By measuring the output voltages from the electrodes 124a-124d fordetecting, acceleration can be detected.

The vibrating body 12 may be polarized partially in an inversedirection. For example, a part which is put between the electrodes 60aand 60b is polarized from the electrode 60a side toward the electrode60b side, and a part which is put between the electrodes 60c and 60d ispolarized from the electrode 60d side toward the electrode 60c side. Inthis case, by applying driving signals having the same phase to theelectrodes 60a, 60b for driving and the electrodes 60c, 60d for driving,it is possible to vibrate the vibrating body 12 in such a manner thatexpansion and contraction take place simultaneously.

When the vibrating body 12 is made of piezoelectric ceramics, the shapeof the electrode is not necessarily plate-shape, and may be, forexample, a comb-like. Similarly, in the acceleration sensor having ashape shown in FIGS. 31-33, the vibrating body may be made ofpiezoelectric ceramics, and electrodes may be formed instead of thepiezoelectric elements.

In the case of the acceleration sensor having a shape shown in FIGS.31-33, when the vibrating body is made of piezoelectric ceramics,electrodes are formed instead of the piezoelectric elements 14a-14d. Thevibrating body is polarized partially in a different direction. That is,the vibrating body is polarized in the direction perpendicular to theopposed electrodes. Therefore, the vibrating body has two parts whichare polarized at a right angle with each other. In such an accelerationsensor, by applying driving signals to the electrodes, the vibratingbody can be vibrated such that longitudinal expansion and contractiontake place simultaneously. The phase of driving signals is decided bythe polarizing direction of the vibrating body and connecting mode ofoscillation circuit.

FIG. 37 is a perspective view showing another example of an accelerationsensor which can detect acceleration in a plurality of directions, andFIG. 38 and FIG. 39 are the sectional views taken along the linesXXXVIII--XXXVIII and XXXIX--XXXIX respectively. The acceleration sensor100 includes a first vibrating body 12a in a rectangular plate shape. Asecond vibrating body 12b in a rectangular plate shape is formed at alongitudinal end of the first vibrating body 12a. The first vibratingbody 12a and the second vibrating body 12b are arranged so that thesurface of the first vibrating body 12a and the surface of the secondvibrating body 12b are crossed at a right angle on one central axis. Thefirst vibrating body 12a and the second vibrating body 12b may beconnected, for example, by welding or soldering. The connected firstvibrating body 12a and second vibrating body 12b may be formed bystamping the metal plate and by twisting it at the center.

Piezoelectric elements 14a, 14b are formed on opposite surfaces of thefirst vibrating body 12a, and piezoelectric elements 14c, 14d are formedon opposite surfaces of the second vibrating body 12b. In thepiezoelectric elements 14a-14d, piezoelectric plates 16a, 16b arepolarized from the outside surface toward the first vibrating body 12aside, and piezoelectric plates 16c, 16d are polarized from the secondpiezoelectric body 12b side toward the outside surface.

The first vibrating body 12a is supported with a first frame 104a. Thefirst frame 104a is formed in a U-shape, and the first vibrating body12a is fixed to the center portion of the first frame 104a. The firstvibrating body 12a is connected with the first frame 104a at both widthends. Hence, a hole 126a is made at the connecting part of the firstvibrating body 12a and the first frame 104a. Weights 120 are formed atthe end portion of the first vibrating body 12a.

Similarly, the second vibrating body 12b is supported with a secondframe 104b. The second frame 104b is formed in a U-shape, and the secondvibrating body 12b is fixed to the center portion of the second frame104b. The second vibrating body 12b is connected with the second frame104b at both width ends. Hence, a hole 126b is made at the connectingpart of the second vibrating body 12b and the second frame 104b. Weights120 are formed at the end portion of the second vibrating body 12b.

As shown in FIG. 40, the first frame 104a and the second frame 104b areheld by a ring-shaped holding member 128. At the position correspondingto the connecting part of the first vibrating body 12a and the secondvibrating body 12b, each frame 104a, 104b is held by the holding member128.

When the acceleration sensor 100 is used, as shown in FIG. 41, anoscillation circuit 110 is connected to the piezoelectric elements 14a,14b, 14c, 14d via resistors 108a, 108b, 108c, 108d. The piezoelectricelements 14a, 14b are connected to the first differential circuit 112,and the piezoelectric elements 14c, 14d are connected to the seconddifferential circuit 114.

When the acceleration sensor 100 is used, the driving signal having thesame phase is applied to the piezoelectric elements 14a, 14b, 14c, 14d.Then, each vibrating body 12a, 12b is vibrated in a longitudinaldirection. As indicated with the solid line arrow in FIG. 37, when thefirst vibrating body 12a expands, the second vibrating body 12bcontracts. Also, as indicated with the one dot chain line arrow in FIG.37, when the first vibrating body 12a contracts, the second vibratingbody 12b expands. Hence, displacement at both ends of the vibratingbodies 12a, 12b is offset, and the vibration leakage to the frames 104a,104b is small because the end of the frame side of each vibrating body12a, 12b does not displace. Therefore, a stabilized vibration can beobtained.

By vibrating the first vibrating body 12a and the second vibrating body12b, inertia is applied to the vibrating bodies 12a, 12b.

When acceleration is applied to, for example, the acceleration sensor100 perpendicular to the surface of the first vibrating body 12a, thefirst vibrating body 12a bends in a direction perpendicular to itssurface as shown in FIG. 42. In this time, since acceleration is appliedto the second vibrating body 12b in a width direction, the secondvibrating body 12b does not bend. Since one longitudinal end of thesecond vibrating body 12b is supported at both width ends with thesecond frame 104b, swing of the second vibrating body 12b is preventedas compared with the case, for example, of being supported at the centerof the second vibrating body 12b. For preventing the swing of the secondvibrating body 12b in a width direction, the whole end portion of thesecond vibrating body 12b may be supported with the second frame 104b.In this case, the hole 126b is not made.

Bending of the first vibrating body 12a interferes with the vibration ofthe first vibrating body 12a, and results in variation of the resonancecharacteristics. By measuring the variation of resonancecharacteristics, acceleration can be detected. In order to detect theacceleration, the voltages generated in the piezoelectric elements 14a,14b are measured. The output voltages of the piezoelectric elements 14a,14b are measured by the first differential circuit 112. When noacceleration is applied to the acceleration sensor 100, the same voltagehaving the same phase is generated in each piezoelectric element 14a,14b. Hence, the output of the first differential circuit 112 becomeszero. When acceleration is applied to the acceleration sensor 100 andthe first vibrating body 12a is bent, voltages having the inverse phaseare generated in the opposed piezoelectric elements 14a, 14b. Bymeasuring the difference between the output voltages of the opposedpiezoelectric elements 14a, 14b, a high output voltage can be obtainedfrom the first differential circuit 112. Therefore, the acceleration inthe direction perpendicular to the surface of the first vibrating body12a can be detected with a high sensitivity. The driving signal appliedto the piezoelectric elements 14a, 14b is offset in the firstdifferential circuit 112, the output signal from the first differentialcircuit 112 does not contain the driving signal.

When acceleration is applied to, for example, the acceleration sensor100 perpendicular to the surface of the second vibrating body 12b, thesecond vibrating body 12b bends in a direction perpendicular to itssurface, as shown in FIG. 43. The acceleration can be detected bymeasuring the difference between the output voltages generated in thepiezoelectric elements 14c, 14d. At this time, since acceleration isapplied to the first vibrating body 12a in a width direction, onelongitudinal end of the first vibrating body 12a is supported at bothwidth ends with the first frame 104a for preventing the swing of thefirst vibrating body 12a due to the acceleration. Needless to say, thewhole end portion of the first vibrating body 12a may be supported withthe first frame 104a. In this case, the hole 126a is not formed.

When acceleration, which is not perpendicular to the surfaces of thefirst vibrating body 12a and the second vibrating body 12b, is appliedto the acceleration sensor 100, the vibrating bodies 12a and 12b aredeformed corresponding to the acceleration components perpendicular tothe surfaces of the vibrating bodies 12a, 12b. Therefore, from the firstdifferential circuit 112 and the second differential circuit 114,signals corresponding to the acceleration components perpendicular tothe surfaces of the vibrating bodies 12a, 12b can be obtained. Fromthese output signals, the acceleration in all directions perpendicularto the center axis of the first vibrating body 12a and the secondvibrating body 12b can be detected.

In the acceleration sensor 100, since weights 120 are formed at the endportions of the vibrating bodies 12a, 12b, when the first vibrating body12a or the second vibrating body 12b is bent, the bending is enlarged bythe mass of the weights 120. Therefore, even when a minute accelerationis applied to the acceleration sensor, a large output signal can beobtained, and the acceleration sensor having high detection sensitivitycan be obtained.

In the acceleration sensor 100, since vibrating bodies 12a, 12b areformed in a plate-shape, large bending from the acceleration can beobtained as compared with the vibrating body formed in a prism shape.Therefore, as compared with the acceleration sensor using a prism-shapedvibrating body, the large output signal from the acceleration can beobtained, and results in a high sensitivity.

As shown in FIG. 44 and FIG. 45, it is possible to form otherpiezoelectric elements 66a, 66b and other piezoelectric elements 66c,66d to the first vibrating body 12a and the second vibrating body 12b.The piezoelectric elements 14a, 14b and the piezoelectric elements 14c,14d are used for driving, and the piezoelectric elements 66a, 66b andthe piezoelectric elements 66c, 66d are used for detecting. In thiscase, by measuring the output voltages of the piezoelectric elements66a, 66b and the piezoelectric elements 66c, 66d, the accelerationapplied to the acceleration sensor 100 can be detected.

In such an acceleration sensor, it is possible to polarize allpiezoelectric elements 14a-14d in the same direction. That is, thepiezoelectric elements 14a, 14b, 14c, 14d may be polarized from theoutside surface toward the vibrating body side, and the piezoelectricelements 14a, 14b, 14c, 14d may be polarized from the vibrating bodyside toward the outside surface. In such cases, the driving signalsapplied to the piezoelectric elements 14a, 14b and the driving signalsapplied to the piezoelectric elements 14c, 14d have inverse phases. Inthis way, the first vibrating body 12a and the second vibrating body 12bcan be vibrated in such a manner that longitudinal expansion andcontraction take place inversely.

As the material of the vibrating body 12a and 12b, piezoelectricceramics may be used. In this case, as shown in FIG. 46 and FIG. 47,electrodes 60a, 60b, 60c, 60d are formed instead of the piezoelectricelements. The vibrating body 12a is polarized in a directionperpendicular to the electrodes 60a, 60b, and the vibrating body 12b ispolarized in a direction perpendicular to the electrodes 60c, 60d. Byapplying the driving signals to the electrodes 60a, 60b and to theelectrodes 60c, 60d, it is possible to vibrate the vibrating bodies 12a,12b in such a manner that longitudinal expansion and contraction takeplace simultaneously. The phase of driving signals is decided by thepolarizing direction of the vibrating body and connecting mode of theoscillation circuit. By measuring the output voltages of the electrodes60a-60d, the acceleration can be detected. Similarly, as to theacceleration sensor having the shape as shown in FIG. 44 and FIG. 45,the vibrating bodies may be made of piezoelectric ceramics, andelectrodes may be formed instead of the piezoelectric elements.

The vibrating body 12a and the vibrating body 12b may not be cross at aright angle with each other. If the surfaces of the vibrating bodies12a, 12b are crossed with each other, it is possible to detect theacceleration components perpendicular to the surfaces, and theacceleration in all directions can be calculated from the accelerationcomponents and the angle between the vibrating bodies 12a and 12b. Thenumber of vibrating bodies is not always two, and more than threevibrating bodies may be connected on one center axis. In this case, ifthe direction of the surface of each vibrating body is made difference,the acceleration in a plurality of directions can be detected. Even inthe case of the acceleration sensor using more than three vibratingbodies, it is possible to prevent vibration leakage to the frame byvibrating the vibrating bodies in such a manner that longitudinalexpansion and contraction take place inversely at the both sides of thecenter of the connected vibrating bodies. The acceleration sensor havinga high sensitivity can therefore be obtained.

Though the end portions of the vibrating bodies 12a, 12b are supportedat both width ends with the frames 104a, 104b, the supporting method isnot always limit to the method using the extending parts at both widthends of the vibrating bodies 12a, 12b in a longitudinal direction asshown in FIG. 37. For example, each of the vibrating bodies 12a, 12b maybe supported with the frames 104a, 104b by extending diagonally fromboth width ends toward the frame. Each of the vibrating bodies 12a, 12bmay be supported with the frames 104a, 104b by extending in a widthdirection of the vibrating body from both width ends toward the frame.Though the frames 104a, 104b are formed in parallel on both sides of thevibrating bodies 12a, 12b, they may be formed on one side of thevibrating bodies 12a, 12b.

FIG. 48 is a perspective view showing another embodiment of anacceleration sensor which can detect the acceleration in a plurality ofdirections, and FIG. 49 is its sectional view. An acceleration sensor100 includes a rectangular plate-shaped first vibrating body 12a. At alongitudinal end of the first vibrating body 12a, a rectangularplate-shaped second vibrating body 12b is formed. The first vibratingbody 12a and the second vibrating body 12b are arranged in a foldedmanner. The first vibrating body 12a and the second vibrating body 12bare connected at both width ends and at the center portion. Hence, twoholes 130 are made side by side between the first vibrating body 12a andthe second vibrating body 12b. The first vibrating body 12a and thesecond vibrating body 12b may be connected by, for example, welding orbonding. The first vibrating body 12a and the vibrating body 12b may beformed by stamping a metal plate and folding it at the center portion.

Piezoelectric elements 14a, 14b are formed on opposite surfaces of thefirst vibrating body 12a. Piezoelectric elements 14c, 14d are formed onopposite surfaces of the second vibrating body 12b. In the piezoelectricelements 14a-14d, for example, piezoelectric plates 16a, 16b arepolarized from the outside surface toward the first vibrating body 12aside, and the piezoelectric plates 16c, 16d are polarized from thesecond vibrating body 12b side toward the outside surface.

The first vibrating body 12a is supported with a first frame 104a. Thefirst frame 104a is formed in a U-shape, and the first vibrating body12a is fixed to the center portion of the first frame 104a. A hole 126ais made at the connecting portion of first vibrating body 12a and thefirst frame 104a. Weights 120 are formed at the end side of the firstvibrating body 12a.

Similarly, the second vibrating body 12b is supported with a secondframe 104b. The second frame 104b is formed in a U-shape, and the secondvibrating body 12b is fixed to the center portion of the second frame104b. A hole 126b is made at the connecting portion of second vibratingbody 12b and the second frame 104b. Weights 120 are formed at the endside of the second vibrating body 12b.

The first frame 104a and the second frame 104b are connected in a foldedmanner at a right angle with each other just like the first vibratingbody 12a and the second vibrating body 12b. When the acceleration sensor100 is used, the connecting portion between the first frame 104a and thesecond frame 104b is held.

When the acceleration sensor 100 is used, as shown in FIG. 50, anoscillation circuit 110 is connected to the piezoelectric elements 14a,14b, 14c and 14d via the resistors 108a, 108b, 108c and 108d. Thepiezoelectric elements 14a and 14b are connected to a first differentialcircuit 112, and the piezoelectric elements 14c and 14d are connected toa second differential circuit 114.

When the acceleration sensor 100 is used, driving signals having a samephase are applied from the oscillation circuit 110 to the piezoelectricelements 14a, 14b, 14c and 14d. By the driving signals, as shown withthe arrows in FIG. 51, when the first vibrating body 12a expands, thesecond vibrating body 12b contracts. As shown with the arrows in theFIG. 52, when the first vibrating body 12a contracts, the secondvibrating body 12b expands. In this way, the first vibrating body 12aand the second vibrating body 12b vibrate in the longitudinal directionsthereof. In this case, as shown with the arrows in FIG. 51 and FIG. 52,the vicinity of the connecting portion of the first vibrating body 12aand the second vibrating body 12b is displaced so as to fold and bend inthe longitudinal directions of each vibrating body. Since thedisplacement of end portion of each vibrating body 12a, 12b is offset,and the end portion of each vibrating body 12a, 12b at the frame side isnot displaced, this results in less vibration leakage to each frame104a, 104b. Therefore, a stabilized vibration can be obtained.

By vibrating the first vibrating body 12a and the second vibrating body12b, inertia is applied to these vibrating bodies 12a and 12b. When anacceleration is applied to the acceleration sensor 100 in the directionperpendicular to the surface of the first vibrating body 12a under thiscondition, as shown in FIG. 53, the first vibrating body 12a bends inthe direction perpendicular to its surface. In this case, since theacceleration is applied in the longitudinal direction of the secondvibrating body 12b, the second vibrating body 12b does not bend. Sincethe second vibrating body 12b is supported at both width ends with thesecond frame 104b, swinging of the second vibrating body 12b in thewidth direction is prevented as compared with the case of beingsupported at the center of the second vibrating body 12b. Since thefirst vibrating body 12a and the second vibrating body 12b are connectedat both width ends and at the center portions, as compared with a caseof connecting at only the center portions, twisting at the connectingportions can be prevented. In order to prevent a width swing of thesecond vibrating body 12b, the whole end portions of the secondvibrating body 12b may be supported with the second frame 104b. In thiscase, the hole 126b is not formed. Also, the connecting portion of thefirst vibrating body 12a and the second vibrating body 12b may beconnected at the whole portion in the widthwise direction. In this case,the holes 130 are not formed.

Bending of the first vibrating body 12a interferes with the vibrating ofthe first vibrating body 12a, and results in a variation of theresonance characteristics. By measuring the variation of the resonancecharacteristics, the acceleration can be detected. In order to detectthe acceleration, similarly to the acceleration sensor shown in FIG. 41,voltages generated in the piezoelectric elements 14a, 14b are measuredby the first differential circuit 112.

When an acceleration is applied to the acceleration sensor 100 in thedirection perpendicular to the surface of the second vibrating body 12b,the second vibrating body 12b is bent as shown in FIG. 54. By measuringthe difference between the output voltages generated in thepiezoelectric elements 14c and 14d by the second differential circuit114, the acceleration can be detected. In this case, in order to preventswinging of the first vibrating body 12a, the first vibrating body 12ais supported with the first frame 104a at the both width ends. Howeverthe whole end portion of the first vibrating body 12a may be supportedwith the first frame 104a. In this case, the hole 126a is not made.

When acceleration, which is not perpendicular to the surfaces of thefirst vibrating body 12a and the second vibrating body 12b, is appliedto the acceleration sensor 100, the vibrating bodies 12a and 12b aredeformed corresponding to the acceleration components perpendicular tothe surfaces of the vibrating bodies 12a, 12b. Therefore, from the firstdifferential circuit 112 and the second differential circuit 114,signals corresponding to the acceleration components perpendicular tothe surfaces of the vibrating bodies 12a, 12b can be obtained. Fromthese output signals, the acceleration in all directions perpendicularto the connecting line of the first vibrating body 12a and the secondvibrating body 12b.

In the acceleration sensor 100, since weights 120 are formed at the endportions of the vibrating bodies 12a, 12b, when the first vibrating body12a or the second vibrating body 12b is bent, the bending is enlarged bythe mass of the weights 120. Therefore, even when a minute accelerationis applied to the acceleration sensor, a large output signal can beobtained, and the acceleration sensor having high detection sensitivitycan be obtained.

In the acceleration sensor 100, the vibrating bodies 12a, 12b are formedin a plate-shape, large bending against the acceleration can be obtainedas compared with the vibrating body formed in a prism-shape. Therefore,as compared with the acceleration sensor using a prism-shaped vibratingbody, a large output signal against the acceleration can be obtained,and results in a high sensitivity.

As shown in FIG. 55, it is possible to form other piezoelectric elements66a, 66b and other piezoelectric elements 66c, 66d to the firstvibrating body 12a and the second vibrating body 12b. The piezoelectricelements 14a, 14b and the piezoelectric elements 14c, 14d are used fordriving, and the piezoelectric elements 66a, 66b and the piezoelectricelements 66c, 66d are used for detecting. In this case, by measuring theoutput voltages of the piezoelectric elements 66a, 66b and thepiezoelectric elements 66c, 66d, the acceleration applied to theacceleration sensor 100 can be detected.

In such an acceleration sensor 100, it is possible to polarize allpiezoelectric elements 14a-14d in the same direction. That is, thepiezoelectric elements 14a, 14b, 14c, 14d may be polarized from theoutside surface toward the vibrating body side, and the piezoelectricelements 14a, 14b, 14c, 14d may be polarized from the vibrating bodyside toward the outside surface. In such cases, the driving signalsapplied to the piezoelectric elements 14a, 14b and the driving signalsapplied to the piezoelectric elements 14c, 14d have inverse phase. Inthis way, the first vibrating body 12a and the second vibrating body 12bcan be vibrated in such a manner that longitudinal expansion andcontraction take place inversely.

As the material of the vibrating body 12a and 12b, piezoelectricceramics may be used. In this case, as shown in FIG. 56, electrodes 60a,60b, 60c, 60d are formed instead of the piezoelectric elements 14a-14d.The vibrating body 12a is polarized in a direction perpendicular to theelectrodes 60a, 60b, and the vibrating body 12b is polarized in adirection perpendicular to the electrodes 60c, 60d. By applying thedriving signals to the electrodes 60a, 60b, and to the electrodes 60c,60d, it is possible to vibrate the vibrating bodies 12a, 12b in such amanner that longitudinal expansion and contraction take placesimultaneously. The phase of the driving signals is decided by thepolarizing direction of the vibrating body and connecting mode of theoscillation circuit. By measuring the output voltages of the electrodes60a-60d, the acceleration can be detected.

Similarly, as to the acceleration sensor having the shape as shown inFIG. 55, the vibrating bodies may be made of piezoelectric ceramics, andelectrodes may be formed instead of the piezoelectric elements.

The vibrating body 12a and the vibrating body 12b may not be cross at aright angle with each other. If the the vibrating bodies 12a, 12b areconnected with each other in a folded manner, it is possible to detectthe acceleration components perpendicular to the surfaces, and theacceleration in all directions can be calculated from the accelerationcomponents and the angle between the vibrating bodies 12a and 12b.

While the present invention has been particularly described and shown,it is to be understood that such description is used merely as anillustration and example rather than limitation, and the spirit andscope of the present inventions are determined solely by the terms ofthe appended claims.

What is claimed is:
 1. An acceleration sensor comprising:a plurality ofplate-shaped vibrating bodies made of piezoelectric material connectedin a folded manner; and electrodes formed on surfaces of said vibratingbodies, wherein said vibrating bodies vibrate in such a manner thatlongitudinal expansion and contraction take place inversely at bothsides a folding portion of said vibrating bodies by applying a drivingsignal to said electrodes.
 2. An acceleration sensor according to claim1, wherein two said vibrating bodies are connected in a folded manner ata right angle, and a pair of said electrodes are formed on oppositesurfaces of each of said vibrating bodies.
 3. An acceleration sensoraccording to claim 1 which further comprises frames connected with eachother for supporting said vibrating bodies.
 4. An acceleration sensoraccording to claim 2, wherein each of said vibrating bodies is polarizedin an direction perpendicular to said electrodes.
 5. An accelerationsensor according to claim 3, wherein each of said vibrating bodies ispolarized in an direction perpendicular to said electrodes.
 6. Anacceleration sensor according to claim 2, wherein driving signals havinginverse phase are applied to two said pairs of said electrodes on saidvibrating bodies.
 7. An acceleration sensor according to claim 3,wherein driving signals having inverse phase are applied to two pairs ofsaid electrodes on said vibrating bodies.